Cellular radiotelephone signal with additional channel assigned to downlink, corresponding method, system, mobile and base station

ABSTRACT

The invention concerns a cellular radio telephone signal comprising a symmetrical two-way main channel, including a main uplink and a main downlink, in particular transmitting low or medium speed data and signalling and control data, and comprising at least one additional channel solely assigned to the downlink, transmitting in particular, high speed data transmission. At one given time, all or part of said supplementary channel transmission capacity can be dynamically allocated to a particular mobile station. Information for retrieving data intended for a particular mobile station and carried by said supplementary channel can be transmitted among said main downlink signalling and control data.

The field of the invention is that of cellular radiotelephony. Moreexactly, the invention concerns data transmission, particularly at highspeeds, in a radiotelephone system.

Known radiotelephone systems, such as the G. S. M. are essentiallydedicated to voice communications. They implement two symmetrical links:a downlink (from a terrestrial base station to a mobile station) and anuplink (from the mobile station to the base station).

Systems under development are also based on such a structure. Thus, thestandard UMTS defined by the ETSI provides for a symmetrical divisionbetween the downlink and the uplink.

The invention applies particularly to these systems. It can also beapplied to satellite systems (GLOBALSTAR, ICO, IRIDIUM, etc.).

One of the problems to which radiotelephone systems will have to find aresponse in years to come, is the advent of new services and newapplications, presupposing very high speed data transmission. Recentstudies thus show that the resource allocated to data transfers (files,sounds, fixed or animated images), particularly via the Internetnetwork, or similar networks, will represent a preponderant part of theresource available, from the year 2005 onwards, and higher, in the end,than the resource allocated to voice communications which should remainapproximately constant.

A particular object of the invention is to bring a solution adapted tothese new needs.

More exactly, an objective of the invention is to provide new cellularradiotelephone technology, allowing high speed data transmission, toradiotelephone mobile stations.

Another objective of the invention is to provide technology of thiskind, which is compatible with known standards, and in particular theUMTS standard as defined by the ETSI.

Another objective of the invention is to provide technology of thiskind, which optimises the use of the resource available, and which isbased on a transmission method particularly adapted to high speed datatransmission. Particularly, an objective of the invention is to offer anavailable speed of at least 6 Mbits/s.

Another objective of the invention is to provide technology of thiskind, which allows technically relatively simple and thereforeinexpensive mobile stations to be made, which are adapted to receivedifferent types of data (voice communications and high speed dataparticularly).

Another objective of the invention is to provide technology of thiskind, allowing high speed data reception, even in unfavourable receptionconditions (high displacement rate, of the order of at least 250 km/h,and multiple paths particularly).

Still another objective of the invention is to provide technology ofthis kind, which allows an optimised and flexible allocation of thetransmission resource, between one or more mobile stations, at a givenmoment. In particular, an objective of the invention is to allow thesharing of the high speed transmission resource between severaloperators.

These objectives, as well as others which will emerge subsequently, aremet according to the invention by means of a cellular radiotelephonesignal, of the type including a main symmetrical bidirectional channel,including a main uplink and a main downlink, providing in particular lowor medium speed transmission of signalling and control data andinformation, and also including at least one additional channel solelyassigned to the downlink, providing in particular high speed datatransmission.

The invention therefore proposes an entirely new signal structure, inthe context of radiotelephony, and more generally telephony systems.Indeed, all these systems are based on a symmetrical structure (based onthe structure of voice communications). On the other hand, thetechnology of the invention is based on an entirely new, asymmetricalapproach, which proves particularly adapted to new high speedapplications.

In other words, the invention proposes the addition, to a conventionalsymmetrical channel, of a downlink only additional channel, dedicated tohigh speed data transmission, such as files transmitted on the Internetnetwork.

It is appropriate to note that this solution is not obvious. It is basedon a new analysis of radiotelephone systems, counter to the usualpractices of the professional.

Although in what follows only one additional channel is considered, itis plain that several channels (corresponding for example to severalfrequency bands) are conceivable.

Preferentially, at a given moment, all or part of the transmissioncapacity of said additional channel is allocated dynamically to aparticular mobile station.

Thus, the resource is allocated dynamically, only when required. It maybe shared, frequentially and/or temporally, between several mobilestations. When demand is not heavy, only one part of the resource(frequentially or temporally) is allocated.

To do this, information allowing the retrieval of data intended for aparticular mobile station and carried by said additional channel is, toadvantage, transmitted among said signalling and control information ofsaid main downlink.

According to an advantageous characteristic of the invention, said maindown channel and said additional channel have synchronous framestructures.

This allows synchronisation of the mobile station to be recovered fromone of the channels (in particular the main channel) and for it to beapplied directly to the other channel (in particular the additionalchannel). This is advantageous in particular when one of the channelsimplements a technique allowing a recovery of simple and precisesynchronisation (the case of CDMA particularly).

According to an advantageous embodiment of the invention, saidadditional channel also provides the transmission of signalling andcontrol information.

Particularly, said additional channel can provide at least thetransmission of signalling and control information intended for themobile station(s) in the method of transmitting data intended for saidmobile station, on said additional channel.

For example, when said additional channel carries high speed dataintended for said mobile station, said signalling and controlinformation intended for a mobile station is duplicated or switched fromsaid main downlink onto said additional channel.

Thus, the mobile may receive, at a given moment, only one or other ofthe channels. This allows the structure of the receiver to beconsiderably simplified, by sharing at least a part of the receptionmeans.

According to a particular embodiment of the invention, said main channelimplements a spread spectrum access technology (CDMA). Particularly, theinvention applies to the UMTS system.

Furthermore, to advantage, said additional channel implements amulti-carrier technology providing distribution of the data in thetime/frequency space.

By multi-carrier technology is meant the implementation of a multiplexof carrier frequencies (for example according to OFDM technology).

In particular, said additional channel implements to advantage the“IOTA” modulation technology, the complex envelope of which responds tothe following equation:${x(t)} = {\sum\limits_{m,n}{a_{m,n}\quad i^{m + n}{{\mathfrak{J}}\left( {t - {n\quad T}} \right)}\quad{\mathbb{e}}^{{\mathbb{i}}\quad\pi\quad m\quad{t/T}}}}$where:

-   -   .m is an integer representing the frequential dimension;    -   .n is an integer representing the temporal dimension;    -   .t represents time;    -   .T is the time symbol;    -   .a_(m,n) is a real digital coefficient chosen from a pre-set        alphabet;    -   .ℑ is the prototype IOTA function (as defined in FR-95 05455,        corresponding to U.S. Ser. No. 08/952,331.

To advantage, the transmission capacity of said additional channel isallocated to a given mobile station, dynamically, in the form of atleast one “block” defined in the time/frequency space.

By “block” is meant in this instance a subset of the time/frequencyspace, defined by a given time interval and a frequency band. Morecomplex geometric structures than a “block” are of course conceivable(and possibly decomposable into a “sub-block”).

Preferentially, said signalling and control information of said maindownlink includes retrieval information of said blocks in thetime/frequency space.

According to an embodiment of the invention, at least some of saidblocks carry temporal and/or frequential synchronisation references.

This may particularly prove useful when high speed data is transmittedover a substantial period of time. These references may be used tomaintain the previously acquired synchronisation.

The invention also concerns cellular radiotelephone systems and methodesimplementing such a signal.

The invention further concerns the mobile stations of such a cellularradiotelephone system. This mobile station includes in particularreception means of at least one additional channel solely assigned tothe downlink, providing in particular high speed data transmission.

According to a preferential embodiment, such a mobile station includessingle synchronisation means implementing an analysis of said mainchannel and delivering synchronisation information to methoding means ofsaid main channel and to methoding means of said additional channel.

Thus, the realisation and implementation of the mobile station aresimplified.

In an advantageous embodiment, the mobile station includes a singlereception link including particularly transposition means onto anintermediate frequency of a received signal and demodulation means ofthe transposed signal, said received signal being able to be selectivelysaid main downlink or said additional channel.

To advantage, the mobile station also includes recovery means of saidsignalling and control information selectively on said main downlink oron said additional channel.

Thus, it is possible to share a part of the reception means between thetwo channels.

Lastly, the invention also concerns the base stations of such a cellularradiotelephone system, including particularly emission means of at leastone additional channel solely assigned to the downlink, ensuring inparticular high speed data transmission.

To advantage, such a base station includes transmission means ofsignalling and control information intended for a given mobile stationon said additional channel, when the latter carries high speed dataintended for said mobile station.

Other characteristics and advantages of the invention will emerge moreclearly from reading the following description of a preferentialembodiment, given as an illustrative and non-restrictive example, andthe appended drawings, among which:

FIG. 1 evokes the allocation of frequency bands according to the UMTSstandard and shows the way in which it can be adapted for the signal ofthe invention;

FIG. 2 shows an example of allocation of the high speed resource of thesignal of FIG. 1;

FIG. 3 shows a block diagram of a first embodiment of a mobile receiveraccording to the invention;

FIG. 4 shows a block diagram of a second embodiment of a mobile receiveraccording to the invention.

As already mentioned, market research on the UMTS has shown that datatransmission would represent 80% of the total traffic by 2005, against20% only for the voice. Data traffic would therefore be, as aconsequence, to a very large extent, asymmetrical, with a heavypreponderance of the downlink (Internet).

The signal and the system of the invention meet this type of need.

In the embodiment described below, the invention is based on the UMTSstandard defined by the ETSI. It therefore uses the following frequencybands, shown in FIG. 1:

1900-1920 MHz: TD-CDMA system in TDD (Time Division Duplex). This bandis used for domestic applications (“cordless”);

-   -   1920-1980 MHz: WCDMA system (“Wideband Code Division Multiple        Access”), uplink;    -   1980-2010 MHz: mobile satellite system (ICO), uplink;    -   2010-2025 MHz: high speed data transmission system, downlink,        specific to the invention;    -   2110-2170 MHz: WCDMA system (“Wideband Code Division Multiple        Access”), downlink;    -   2170-2200 MHz: mobile satellite system (ICO), downlink.

It may be noted therefore that the allocation of resources provided forby the ETSI is, conventionally, symmetrical. Indeed there is clearly:

-   -   a downlink 11 ₁ and an uplink 11 ₂ each of 60 MHz for exchanges        according to W-CDMA technology;    -   a downlink 12 ₁ and an uplink 12 ₂ each of 30 MHz for exchanges        by satellite (ICO);    -   two TD-CDMA links 13 ₁ and 13 ₂, whose role was not yet defined        and for which the invention proposes a particular        implementation.

According to the invention, a combination of channels is used. To obtainan asymmetrical system, a low speed WCDMA (11 ₁ and 11 ₂) symmetricalchannel and a high speed downlink transmission channel using amulti-carrier system 13 ₂ are combined.

The link 13 ₁ is for example assigned to domestic applications. For thedownlink according to the invention preferentially the link 13 ₂ isselected which is frequentially separated from the W-CDMA link 11 ₂,which allows easy separation, by filtering, of the two links.

The link 13 ₂ may use a conventional multi-carrier modulation, such asthat implemented in OFDM systems (see for example the DAB (“DigitalAudio Broadcasting”) standard for radio broadcasting). Below, the caseis considered of an IOTA modulation, which proves particularly adaptedto the invention. The principle and implementation of the IOTAmodulation are described in patent application FR-95 05455, incorporatedby reference.

To illustrate the principle of the invention, the example is consideredof a user connecting to the Internet network.

When a channel is initially allocated to a user, only the WCDMA channel11 ₁, 112 is really allocated. This channel is a low speed channel (forexample 8 or 16 kbit/s) this channel is used conventionally on theuplink 112, so as to transmit signalling and data issuing from the user.

On the downlink 111, only signalling and low speed data are found aswell as the high speed transmission channel 132 control information.

When the user loads a large file, the network allocates to this user anadditional resource on the IOTA channel 132. This allocation is carriedout dynamically.

The WCDMA down channel 111 transmits control information allowing theadditional resource allocated dynamically to the user concerned to bedescribed.

This resource is described for example as the coordinates of a “block”of the time/frequency plane, in which the data will be transmitted.Below is given a form of definition of these “blocks” in thetime/frequency plane in relation to FIG. 2.

According to a first embodiment, the WCDMA down channel 111 is stillactive. In this case, the IOTA speed channel 132 is used exclusively totransmit data. The signalling is still transmitted via the WCDMA downchannel 111.

A drawback of this first embodiment is that it presupposes thesimultaneous reception of the WCDMA down channel 111 and of the IOTAchannel 132.

A second embodiment overcoming this drawback consists in toggling thetotality of the downlink information (signalling is given) onto the highspeed IOTA channel 132 for the duration of the transmission of theallocated “block”.

In this case, a part of the allocated resource is reserved forsignalling. There is therefore a double “handover” (synchronous) fromthe signalling point of view: a first one to toggle the signalling ontothe IOTA channel 132, as soon as the transmission of a block starts, anda second one to return automatically onto the WCDMA downlink channel111, as soon as the transmission of the “block” is complete.

Downlink information can be switched onto the high speed channel orsimply duplicated (which simplifies transitions during handovers).

This method is more complex to manage, from the signalling point ofview, but, as will emerge subsequently, it simplifies the structure ofthe mobile receiver.

An embodiment of the signal of the invention is now described in moredetail.

The system includes two types of physical channel: WCDMA channels andIOTA channels. To advantage, these two types of channels share a commonframe structure.

For example, the totality of the signals may be described from a common4.096 MHz clock. The transmission unit is the slot (time interval), of aduration of 625 ms. The elementary frame has a duration of 10 ms, thatis 16 slots. A multi-frame of 720 ms is also defined.

The WCDMA channels use a chip rate of 4.096 MHz, that is 2560 chips(signal unit) per slot or 40960 chips per frame. The detailedspecification can be found in the ETSI documentation (see particularly Tdoc SMG 905-97) and ARIB (Association of Radio Industries and Business)“specifications of air interface for a 3G mobile system” (18/12/97). Thesignal emitted comprises particularly all the references necessary forthe temporal and frequential synchronisation of the mobile station.

The IOTA channel uses a time symbol T of 125 ms or of 62.5 ms, that isrespectively 5 or 10 symbols per slot or again 512 or 256 chips persymbol. The spacing between carriers is 4 KHz in the first case and 8KHz in the second case.

IOTA technology is described in detail in patent application FR-95 05455already mentioned. In this document will be found all the informationnecessary for its implementation, for emission and reception.

The equation of the complex envelope of the transmitted signal is then:${x(t)} = {\sum\limits_{m,n}{a_{m,n}\quad i^{m + n}{{\mathfrak{J}}\left( {t - {n\quad T}} \right)}\quad{\mathbb{e}}^{{\mathbb{i}}\quad\pi\quad m\quad{t/T}}}}$where:

-   -   .m is an integer representing the frequential dimension;    -   .n is an integer representing the temporal dimension;    -   .t represents time;    -   .T is the time symbol;    -   .a_(m,n) is a real digital coefficient chosen from a pre-set        alphabet;    -   .ℑ is the prototype IOTA function (as defined in FR-95 05455).

According to the invention, a “block” is defined for example byrelationships of framing the temporal index n and the frequential indexm, as is shown in FIG. 2. A block is allocated to a particular user.

For example, for a given communication, the network is to transmit alarge file. It is allocated the block 21, which corresponds to theresource necessary to transmit the file. The location of this block isretrieved very simply by its two “ends” 251 (m1,n1) and 252 (m2,n2).

Of course, other retrieval methods of data intended for a user areconceivable.

It will be noted that the resource can easily be shared in time (nopresupposition as to what precedes or follows the block 21), and infrequency. According to need, the frequency band can be shared, forexample with the block 22. When there is no need, no transmission iscarried out. Likewise, if only one part of the resource is required, apart of the frequency band 23 is able not be modulated.

A part of the data of the “block” can be reserved for the transmissionof data transmitted the rest of the time on the main channel, asdiscussed below.

Two embodiments of a mobile receiver are now described.

In the first option, there is simultaneous reception of the tworeception bands. The reception links 311 and 312 are simply duplicated.

The aerial 32 is connected to each of the reception links via a duplexer33 having two outputs 341 and 342 corresponding to the bands 2110-2170MHz or 2010-2025 MHz respectively, each output being connected to areception link. This duplexer 33 also includes an input 35 covering theband 1920-1980 MHz. This input is connected to a power amplifier 36.

Each reception link 311, 312 includes:

-   -   a low noise amplifier (LNA) 371 and 372;    -   a mixer 381, 382 and a synthesizer 391, 392 allowing one of the        two previous bands to be transposed into intermediate frequency;    -   an IF filter 3101, 3102 of a bandwidth of the order of 5 MHz;    -   an IQ baseband converter 3111, 3112, controlled by a synthesizer        3121, 3122;    -   an analogue-to-digital converter (ADC) 3131, I, 3131, Q and        3132, I, 3132, Q on each of the I and Q links with a sampling        frequency of 8.192 MHz.

Digital methoding (demodulation, decoding) is carried out by a signalmethodor (DSP) 314 combined with two “hardware” accelerators:

-   -   a correlator for the realisation of the rake filter required for        CDMA signal demodulation (3141);    -   an FFT comethodor for demodulation of IOTA signals (3142).

The DSP, combined with a “hardware” accelerator for modulation, alsogenerates WCDMA signals to be emitted in the form of digital I and Qsamples (3143).

The emission link includes:

-   -   a digital-to-analogue converter 315I, 315Q on each of the I and        Q links with a sampling frequency of 8.192 MHz;    -   an IF modulator 316 controlled by a synthesizer 317;    -   a mixer 318 and a dynamic sythesizer 319 allowing signals to be        transposed into intermediate frequency in the emission band;    -   a power amplifier 36.

The synchronisation of the mobile station for reception of WCDMA signalsuses conventional techniques in this domain, and particularly the Rakefilter for temporal synchronisation.

Once the reference oscillator and the mobile time base have beencompelled, this synchronisation is used directly for the reception ofIOTA signals, for which no additional synchronisation method isrequired.

Thus there is a direct benefit derived from the quality and facility ofsynchronisation of CDMA technology when high speed data is received,without adaptation (the frame structures being the same).

In the second option, there is no simultaneous reception of the tworeception bands. This markedly simplifies the structure of the receiver.The duplexer 33 and the emission link are identical to the first option.They are therefore not subject to further comment.

The receiver includes:

-   -   a low noise amplifier (LNA) 371 connected to the 2170-2200 MHz        output of the duplexer;    -   a low noise amplifier (LNA) 372 connected to the 2010-2025 MHz        output of the duplexer;    -   a switch 41 allowing the two LNA outputs to be switched;    -   a mixer 42 and a double band synthesizer 43 allowing the two        previous bands to be transposed into intermediate frequency;    -   an IF bandpass filter 44 of a bandwidth of the order of 5 MHz;    -   an IQ baseband converter 45 controlled by a synthesizer 46;    -   an analogue-to-digital converter 47I, 47Q on each of the I and Q        bands, with a sampling frequency of 8.192 MHz.

Reception digital methoding 314 is identical to that of the firstoption. On the other hand, there is no simultaneous methoding of WCDMAsignals and of IOTA signals, which reduces the CPU load of the DSPmethodor 314.

The synchronisation of the mobile station for the reception of WCDMAsignals is identical to that described previously. Once the referenceoscillator and the mobile station time base are compelled, this initialsynchronisation is used directly for the reception of IOTA signals, forwhich no additional synchronisation method is required.

However, the reception of WCDMA signals being then interrupted, themaintenance of this synchronisation must however be provided by othermeans. Nonetheless, as a general rule, the transmission of a block isrelatively short, and it is not necessary to re-synchronise the mobilestation, the inherent stability of the reference oscillator being morethan adequate for a few seconds. However, if the allocation is of longduration, it might then be necessary to insert periodically additionaltemporal and frequential synchronisation references.

1. A cellular radiotelephone signal, of the type including a mainsymmetrical bidirectional channel, including a main uplink and a maindownlink, providing in particular low or medium speed transmission ofsignalling and control data and information, characterised in that itincludes at least one additional channel solely assigned to downlink,providing in particular high speed data transmission.
 2. A cellularradiotelephone signal according to claim 1, characterised in that, at agiven moment, all or part of the transmission capacity of saidadditional channel is allocated dynamically to a particular mobilestation.
 3. A cellular radiotelephone signal according to claim 2,characterised in that information allowing the retrieval of dataintended for a particular mobile station and carried by said additionalchannel is transmitted among said signalling and control information ofsaid main downlink.
 4. A cellular radiotelephone signal according to anyone of claims 1 to 3, characterised in that said main channel and saidadditional channel have synchronous frame structures.
 5. A cellularradiotelephone signal according to any one of claims 1 to 4,characterised in that said additional channel also provides fortransmission of signalling and control information.
 6. A cellularradiotelephone signal according to claim 5, characterised in that saidadditional channel provides at least for transmission of signalling andcontrol information intended for mobile station(s) in the method oftransmitting data intended for said mobile station, on said additionalchannel.
 7. A cellular radiotelephone signal according to claim 6,characterised in that, when said additional channel carries high speeddata intended for said mobile station, said signalling and controlinformation intended for a mobile station is duplicated or switched fromsaid main downlink onto said additional channel.
 8. A cellularradiotelephone signal according to any one of claims 1 to 7,characterised in that said main channel implements a spread spectrumaccess technology (CDMA). 9 A cellular radiotelephone signal accordingto any one of claims 1 to 8, characterised in that said additionalchannel implements a multi-carrier technology providing distribution ofdata in the time/frequency space.
 10. A cellular radiotelephone signalaccording to claim 9, characterised in that said additional channel hasa complex envelope responding to the following equation:${x(t)} = {\sum\limits_{m,n}{a_{m,n}\quad i^{m + n}{{??}\left( {t - {n\quad T}} \right)}\quad{\mathbb{e}}^{{\mathbb{i}}\quad\pi\quad m\quad{t/T}}}}$where: .m is an integer representing the frequential dimension; .n is aninteger representing the temporal dimension; .t represents time; .T isthe time symbol; .a_(m,n) is a real digital coefficient chosen from apre-set alphabet; .ℑ is the prototype IOTA function (as defined in FR-9505455).
 11. A cellular radiotelephone signal according to any one ofclaims 9 and 10, characterised in that the transmission capacity of saidadditional channel is allocated to a given mobile station, dynamically,in the form of at least one block defined in the time/frequency space.12. A cellular radiotelephone signal according to claim 11,characterised in that said signalling and control information of saidmain downlink includes retrieval information of said blocks in thetime/frequency space.
 13. A cellular radiotelephone signal according toany one of claims 11 and 13, characterised in that at least some of saidblocks carry temporal and/or frequential synchronisation references. 14.A cellular radiotelephone system of the type implementing a mainsymmetrical bidirectional channel, including a main uplink and a maindownlink, providing in particular low or medium speed transmission ofsignalling and control data and information, characterised in that italso implements at least one additional channel solely assigned to thedownlink, providing in particular high speed data transmission.
 15. Acellular radiotelephone method of the type implementing a mainsymmetrical bidirectional channel, including a main uplink and a maindownlink, providing in particular low or medium speed transmission ofsignalling and control data and information, characterised in that italso implements at least one additional channel solely assigned to thedownlink, providing in particular high speed data transmission.
 16. Amobile station of a cellular radiotelephone system, including emissionmeans of main uplink and reception means of a main downlink, saiduplinks and downlinks forming a main symmetrical bidirectional channelproviding in particular low or medium speed transmission of signallingand control data and information, characterised in that it also includesreception means of at least one additional channel solely assigned tothe downlink, providing in particular high speed data transmission. 17.A mobile station of a cellular radiotelephone system according to claim16, characterised in that it includes single synchronisation meansimplementing an analysis of said main channel and deliveringsynchronisation information to methoding means of said main channel andto methoding means of said additional channel.
 18. A mobile station of acellular radiotelephone system according to any one of claims 16 and 17,characterised in that it includes a single reception link includingparticularly transposition means onto an intermediate frequency of areceived signal and demodulation means of the transposed signal, saidreceived signal being able to be selectively said main downlink or saidadditional channel.
 19. A mobile station of a cellular radiotelephonesystem according to any one of claims 16 to 18, characterised in that itincludes recovery means of said signalling and control informationselectively on said main downlink or on said additional channel.
 20. Abase station of a cellular radiotelephone system, of the type includingreception means of a main uplink and emission means of a main downlink,said uplinks and downlinks forming a main symmetrical bidirectionalchannel providing in particular low or medium speed transmission ofsignalling and control data and information, characterised in that italso includes emission means of at least one additional channel solelyassigned to the downlink, providing in particular high speed datatransmission.
 21. A base station of a cellular radiotelephone systemaccording to claim 20, characterised in that it includes transmissionmeans of signalling and control information intended for a given mobilestation on said additional channel, when the latter carries high speeddata intended for said mobile station.